In television systems, a specific scan format called “interlaced scan format” is widely utilized. Due to the advent of digital television (DTV) signals, deinterlacing is utilized for converting from the interlaced scan format into a progressive scan format for DTV applications. There are two main deinterlacing techniques: an inter-field (or motion-compensated) interpolation technique and an intra-field (or spatial) interpolation technique. The inter-field technique requires more than one field as an input while the intra-field technique requires only one field to process.
FIG. 1 illustrates an example interlaced scan format 100 including a “top” field 102 and a “bottom” field 104, which are scanned in an alternate manner on the TV screen to form the whole picture. Each “field” is formed by a stack of the “existing scan lines” as shown in FIG. 1. Each field (either top or bottom) contains only half the numbers of scan lines of the whole picture, while the other half of scan lines, denoted by “missing scan line” in FIG. 1, are missing from that field.
In FIG. 1, the symbols ◯ denote the pixels on the existing scan lines in both the top and bottom fields 102 and 104. Further, the symbols x denote the pixels on the missing scan lines, in both the top and bottom fields 102 and 104. The main object of the intra-field deinterlacing technique is to interpolate each missing pixel x in both the top and bottom fields from its neighboring existing pixels ◯.
An existing implementation for intra-field deinterlacing includes simple line doubling and vertical line averaging. However, the video qualities of these two implementations produce various artifacts, such as edge jaggedness or edge blurring, making them unsuitable for DTV applications.
A more advanced intra-field deinterlacing technique utilizes edge directed interpolation (EDI). Conceptually, the EDI intra-field deinterlacing technique takes advantage of the direction of edges in an image represented by the two fields, to interpolate the missing pixels. More specifically, the direction of edges associated with each missing pixel is calculated and the set of existing pixels along that calculated edge direction is used to interpolate a missing pixel. The edge detections in many implementations of the EDI intra-field deinterlacing technique are usually determined based on the maximum correlation of a pair of vectors formed by the set of existing pixels immediately above and below the missing pixel.
However, there are many drawbacks to the conventional EDI intra-field deinterlacing technique. First, noise can complicate proper detection of edge direction. Though setting a wider vector can help reduce this effect, it also increases the probability of misdetection in certain areas. Second, in certain areas, such as thin lines and complex detail areas, the vector correlation tends to result in incorrect direction detection. Third, the number of possible directions are limited to a preset number, and directions such as steep angles (close to vertical direction), are usually inaccessible. There is, therefore, a need for a deinterlacing technique that performs edge directed deinterlacing that addresses the above drawbacks.